In internal combustion engines which are to be operated with a fuel which has a high viscosity at low temperatures, the problem exists that by means of such fuels no ignitable mixture can be generated in the combustion chambers of the internal combustion engine for the starting of the internal combustion engine, i.e. for starting up the internal combustion engine at these low temperatures. In so-called “biofuels”, in particular bio diesel, this problem already occurs at temperatures below +14° C. Other biofuels, such as for example ethanol and methanol, are characterized by a flash point of approximately 12° C., which is very high compared with the flash point of conventional petrol, which is at approximately −42°. Consequently, such biofuels have a low volatility compared with petrol and require a high vaporization heat compared with petrol. In such biofuels, such as ethanol and methanol, these characteristics lead to critical situations for the starting of an internal combustion engine under cold environmental conditions, because such biofuels require a great amount of heat in order to generate an injection spray which is suitable for an ignition and for starting the internal combustion engine.
This problem can be countered by two fundamentally different approaches to a solution. In a first solution approach, a second fuel system can be provided for operating the internal combustion engine, which makes it possible to operate the internal combustion engine with a different fuel for its start-up which is also easily ignitable at lower temperatures, in order to thus start it up. However, such a solution is very complex and accordingly expensive. Furthermore, the problem arises here that the vehicle driver must monitor two different fuel tanks or respectively the filling levels thereof, and must also not confuse these when refueling.
A second solution approach is based on the general idea of preheating the fuel which is difficult to ignite for the starting process of the internal combustion engine. By preheating the fuel, its temperature and ignitability are increased. In particular, the viscosity is thereby reduced. The preheating devices named in the introduction come into use in this connection.
From DE 101 40 071 A a separate heating circuit is known for the heating of the fuel, wherein an injection nozzle, which is configured specifically for this, has an additional connection for the heating circuit. Such a solution is complex and requires a comparatively great amount of installation space.
From DE 10 2009 001 062 A it is known to heat the fuel by heated valve air, wherein here, also, a specific injection nozzle is necessary.
From FR 2 876 161 A it is known to integrate a heating device into a fuel distributor rail. Here, a comparatively great volume of fuel is to be heated, in order to be able to provide the preheated fuel for the starting operation. This requires a comparatively great amount of electrical energy and time.
From EP 1 888 910 B1 a fuel injection system is known which has a distributor rail for the provision of liquid fuel. In addition, several preheating devices of the type named in the introduction are provided, which respectively contain a preheating chamber, which respectively have a heating element and which respectively are connected to the distributor rail via an inlet connection. Furthermore, several fuel injectors or injection nozzles are provided, which are respectively connected to such a preheating device via an outlet connection. For each fuel injector a fuel path is thereby produced which leads from the distributor rail through the respective preheating chamber to the respective fuel injector. In the known fuel injection system or respectively in the known preheating device, the respective heating element is configured as a glow rod or glow plug, which projects coaxially into the respective preheating chamber. Furthermore, in the known preheating device a housing containing the respective preheating chamber is made from metal and in the installed state is welded with the distributor rail.